1. Field of the Invention
The invention relates to a MIG/MAG welding machine for pulsed arc welding, comprising a constant voltage source and at least one transistor included in the welding circuit and controlled by a pulse generator with adjustable pulse duration and pulse sequence frequency, wherein the pulse generator with the transistor as an additional apparatus can be included in the supply lines which extend to the welding electrode and the workpiece and are if necessary interconnected on the input side via a capacitor.
2. Background Discussion
For various applications the users of electric welding machines prefer a machine whose welding current is made up of a basic current and a pulse current superimposed thereon, rather than a machine which merely delivers d.c. as the welding current. Welding processes operating with a pulse current superimposed on the basic current arc known as "pulsed are processes".
Welding machines are commercially available which supply a basic current with a superimposed pulse current as the welding current. In such welding machines both the value of the basic current, the value of the pulse current, and the duration of the individual pulses and the pulse sequence frequency can be adjusted. These welding machines, specifically designed for such a welding current, are expensive.
In contrast, a constant voltage source with an additional apparatus can be used as a welding machine more cheaply. In such cases all that many users need to do is to purchase an additional apparatus in addition to their existing constant voltage source. The additional apparatus is designed to provide the pulse output. Since the total welding power is made up of the power of the constant voltage sources and the pulse power of the additional apparatus, as a rule the power of the constant voltage source is not fully utilized, and the welding machine constructed in this way is of excessive size. However, the additional apparatus which must provide the pulse power is also fairly expensive.
These problems do not exist in a known MIG/MAG welding machine of the kind specified, in which the total welding power is provided by the constant voltage source. The or each transistor connected in parallel is either fully operated or completely blocked via an amplifier. In the pauses between the pulses the basic current flows via an ohmic resistor connected in parallel to the transistors (German OS No. 32 17 093 A 1).
In this welding machine the basic current may take on any value during the pauses between the pulses, more particularly it may drop below the small value for maintaining the arc. However, experience shows that currents of the order of magnitude of 30-50 amps are required to maintain the arc. Another disadvantage is that the additional apparatus is connected wrongly poled to the direct voltage source. There is therefore the risk that the transistors may be destroyed.
It is an object of the invention to provide a welding machine of the kind specified which requires the user to have no special operating capacities in order to perform a perfectly satisfactory weld.